The long-range goal of the work described in this proposal is to obtain an understanding of the cellular immune response in humans to infection by adenovirus. Adenovirus is a frequent cause of infections in children, much less so in adults. Suprisingly little is known about the immune response to adenovirus in humans, however, especially the cellular immune response. We have constructed an in vitro system for the generation of a primary cellular immune response to adenovirus and wish to exploit this system to understand the basic immunology of the response. With this in mind, we propose the following specific aims: 1. Test the hypothesis that multiple epitopes within several different adenovirus proteins are the targets of human CTLs, and that these targets vary depending on HLA type. The amino acids within the Ad5 protein(s) that constitute recognition domains will be determined through the use of viral mutants, expression constructs and peptides. These studies will be performed with CTLs from five individuals of differing HLA type to determine the extent to which the epitopes vary depending on which class I and class II molecules are expressed. 2. Test the hypothesis that the epitopes in adenovirus proteins recognized by CTLs will vary depending on the HLA type of the individual. Viral epitopes recognized by various class I and class II HLA molecules will be determined through the analysis of CTL clones. Peptides representing viral epitopes defined in the first specific aim will be fed to target cells matched at one or more loci, and killing by CTL clones will be determined. 3. Test the hypothesis that different subgroups of adenovirus will have some unique, and some similar, CTL epitopes. The epitopes from adenovirus types 11 (subgroup B) and 31 (subgroup A) that elicit CTL responses will be determined to ascertain whether similar or different regions of the viral proteins are targeted. Successful completion of these aims will provide significant new insight into the cellular immune response to adenovirus infections in humans. The practical application of this knowledge could lead to the development of strategies for the toleraization of individuals to Ad5 to increase the efficacy of gene therapy, and to the development of immunotherapies for immunocompromised individuals with life-threatening adenovirus infections.